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Table 2 Fitness-coupled selection pressure for in vivo continuous evolution

From: In vivo continuous evolution of metabolic pathways for chemical production

Type

Selection pressure

Principle

Products

Original yield or titre

Optimised yield or titre

Evolution time, generations

Ref

Natural metabolite production/cell fitness coupling

Hydrogen peroxide

Production of β-carotene as antioxidant to neutralise the oxidative stress of hydrogen peroxide

β-carotene

6 mg g−1 [dcw]

18 mg g−1 [dcw]

40

[79]

LB medium

Coupling ATP and lactate production to growth by engineering lactate production route as the sole anaerobic NADH oxidation route

d-lactate

Maximum production: 865 ± 36 mmol l−1

Yield: 86%

Maximum production: 1071 ± 2 mmol l−1

Yield: 93%

34

[83]

NBS medium with glucose and betaine (optional)

l-lactate

Maximum production: 1228 ± 31 mmol l−1

Yield: 95%

Maximum production: 1314 ± 48 mmol l−1

Yield: 98%

80

[85]

Metabolic evolution

NBS or AM1 medium with glucose

Coupling ATP and growth to alanine production and NADH oxidation

l-alanine

Maximum production: 181 mmol l−1

Yield: 81%

Maximum production: 1279 mmol l−1

Yield: 95%

123

[86]

NBS medium with 9% xylose

D(–)-lactate hydrogenase fermentation pathway as the sole fermentative pathway coupled with the growth of strain

Ethanol

≈ 250 mM

≈ 950 mM

38

[87]

NBS or AM1 medium with glucose

Coupling growth and glucose fermentation to NADH oxidisation pathway

Succinate

108 mM

699 mM

150

[88, 89]

Malate

0 mM

313 mM

Artificial metabolite production/cell fitness coupling

Nickel ion

Riboselector connecting phosphoenolpyruvate to oxaloacetate which is a precursor to lysine

l-lysine

0.0 g l−1

0.6 g l−1

12

[92]

Sodium dodecyl-sulphate (SDS) for positive selection and colicin E1 for negative selection

Sensor-selector connecting a chemical sensor to a cognate promoting operator controlling selector and tolC toggle switch for reverse selection

Naringenin

1.69 mg l−1

61 mg l−1

60a

[90]

Glucaric acid

0.05 mg l−1

1.2 mg l−1

5a

[90]

Maltose

Maltose hydrolase is coupled to tryptophan sensor and the cell is cultured in a medium with maltose as a sole carbon source to couple cell growth to tryptophan production

l-trytophan

0.5 mg l−1 OD −1600

5 mg l−1 OD −1600

12

[95]

N/A

Co-cultivation of auxotroph to couple the growth of secretor strain and sensor strain to amplify the difference in production level. 2-ketoisovalerate auxotroph is used as sensor strain, while lysine auxotroph is used as secretor strain

Isobutanol

1.8 ± 0.1 g l−1

9.4 ± 0.4 g l−1

N/A

[96]

  1. aNumber of cycles of multiplex automated genome engineering (MAGE) followed by toggled selection